1. Field of the Invention
The present invention relates to an imaging apparatus, and, more particularly, to a mechanism for an imaging apparatus, such as an ink jet printer, that provides automated printhead-to-print medium gap spacing.
2. Description of the Related Art
In a typical ink jet printer having a reciprocating printhead, a printhead carriage carrying the printhead is supported by at least one carrier guide rod which is positioned substantially transverse to a print media path. As a sheet of print media is transported in an indexed manner under the printhead, the printhead is scanned in a reciprocating manner across the width of an image area on the sheet of print media, wherein the path of the reciprocating printhead defines a print zone. A platen is provided opposite to the printhead for contacting the non-printed side of the print media and, in part, defines the distance between the printhead and the sheet of print media.
One important parameter associated with an ink jet printer is the gap between the plane of the nozzle plate of the printhead and the plane of the print medium on which the ink expelled from the nozzle plate is deposited. As the gap becomes wider, the error in dot placement increases. The limits on the low end of the gap range is defined by the point at which the printhead actually contacts the media, thereby causing smearing of the freshly deposited ink. In addition, such contact with the print media can result in damage to the printhead such as, for example, by clogging the nozzles of the nozzle plate of the printhead. Thus, it is desirable in a high quality ink jet printer design to set the printhead-to-print medium gap to a optimum minimum value without permitting contact between the printhead and the print medium. However, while an optimum value may be obtained for a particular thickness of print media, any variation in thickness of the print medium, e.g., the difference between the thickness of 20 pound paper and the thickness of card stock or envelopes, results in variations in the printhead-to-print medium gap, which in turn adversely affects print quality.
What is needed in the art is a mechanism for an ink jet printer that provides automated printhead-to-print medium gap spacing.
The present invention provides a mechanism for an imaging apparatus, such as an ink jet printer, that provides automated printhead-to-print medium gap spacing.
The invention comprises, in one form thereof, an imaging apparatus having a printhead positioned above a print media support, wherein a print medium passes therebetween during printing. The imaging apparatus includes a first side frame and a second side frame, the second side frame being spaced apart from the first side frame. A guide rail extends between the first side frame and the second side frame. In addition, a guide rod having a first end, a second end and an axis is provided that extends between the first side frame and the second side frame, the guide rod being positioned to be substantially parallel to the guide rail. A printhead carrier is provided for carrying the printhead. The printhead carrier has a slotted portion for slideably engaging the guide rail and has a bearing for slideably engaging the guide rod. A first eccentric bushing assembly is provided for movably mounting the first end of the guide rod to the first side frame. A second eccentric bushing assembly is provided for movably mounting the second end of the guide rod to the second side frame. A gap spacing adjustment mechanism is coupled to at least one of the first eccentric bushing assembly and the second eccentric bushing assembly for effecting a change in position of the guide rod in a direction normal to the guide rod axis so as to adjust a gap spacing between the printhead and the print medium.
In one preferred form of the invention, the gap spacing adjustment mechanism provides a driven gear coupled to the first eccentric bushing. The gap spacing adjustment mechanism further includes a ratchet mechanism and a drive gear coupled to the ratchet mechanism. The ratchet mechanism includes an actuator for effecting selective rotation of the drive gear in a first rotational direction. The drive gear is positioned for engaging the driven gear to rotatably drive the driven gear to effect a change of position of the carrier guide rod in the direction normal to the guide rod axis so as to adjust the spacing of the printhead-to-print medium gap.
One advantage of the present invention is that the printhead-to-print medium gap spacing is easily adjusted for each thickness of media that can be accommodated by the imaging apparatus.
Another advantage is that the printhead-to-print medium gap spacing can be adjusted automatically with minimal user intervention.
Yet another advantage is that the printhead-to-print medium gap spacing can be optimized for each type of media accommodated by the imaging apparatus.